emerge: there are no ebuilds built with USE flags to satisfy "x11-base/xorg-server[xvfb]".
!!! One of the following packages is required to complete your request:
- x11-base/xorg-server-1.13.0-r1::gentoo (Change USE: +xvfb)
(dependency required by "dev-util/cmake-2.8.10.1[test]" [ebuild])
(dependency required by "app-text/poppler-0.20.5" [installed])
(dependency required by "net-print/cups-1.6.1" [installed])
(dependency required by "@selected" [set])
(dependency required by "@world" [argument])

if I do not install xorg-server and its deps.
Beside dev-libs/glib this is now the 2nd package with requires an installed Xserver installed just for package testing